Shielded winding with cooling ducts

ABSTRACT

Electrical inductive apparatus of the shell-form type, having a plurality of axially spaced, start-start, finish-finish connected, pancake-type coils disposed in a fluid filled tank. A plurality of edge shielding members are disposed to shield the start-start, and finish-finish connections, and the adjacent edges of the pancake coils interconnected thereby. The edge shielding members are spaced from the edges of the pancake coils they are shielding, to enable the fluid to contact the edges of the pancake coils.

Runl'l. Robin 3,376,530 4/1968 Fisher....................i...... 336/84 X Munde, Ind. 3,376,531 4/1968 Fisher et al. 336/84 X 97o FOREIGN PATENTS [45] wanted A 655,329 1/1965 Belgium 336/70 Primary Examiner-Thomas J. Kozma M97811, h Attomeys-A. T. Stratton, F. E. Browder and Donald R.

' Lackey 7 Claims, 6 Drawing Figs.

336/70, 336/84 ABSTRACT: Electrical inductive apparatus of the shell-form [5 ll". Clea-n..-.-.......-.............................-.....--.Holt 7 type having a plurality of spaced sta pstan finish. 7 15/0 finish connected, pancake-type coils disposed in a fluid filled new 336/55, 53, tank. A plurality of edge shielding members are disposed to 60, 84 shield the start-start, and finish-finish connections, and the ad- R f Cm jacent edges of the pancake coils interconnected thereby. The e edge shielding members are spaced from the edges of the pan- UNITED STATES PATENTS cake coils they are shielding, to enable the fluid to contact the 2,724,735 11/1955 Johnston 336/84 X edges ofthe pancake coils.

United States Patent [72] Inventor [22) Filed [73] Assignee Westinghouse Electric Corporation [54] SHIELDED WINDING WITH COOLING DUCTS II lllliv lll I m PATENTED AUG31 1971 I 3502.235.

sum 3 or 3 FIGS.

SHIELDED WINDING WITH COOLING DUCTS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates in general to electrical inductive apparatus of the shell-form type, such as power transformers, and more specifically to insulating and edge shielding structures for the electrical windings thereof.

2. Description of the Prior Art Electrical inductive apparatus of the shell-form type, such as power transformer, includes a magnetic core-winding assembly disposed in a fluid filled tank. The electrical windings include a plurality of axially spaced pancake type coils, which are cooled by the fluid, such as mineral oil. The pancake coils are disposed on a horizontal axis, to provide vertical cooling ducts between them, with the fluid circulating upwardly through the ducts by the natural thermal-siphon effect, or under the influence of a pump, as desired.

The pancake coils must be mechanically braced to withstand short circuit mechanical stresses, they. must be electrically insulated to accommodate electrical stresses, and these objectives must be achieved while maintaining adequate flow of the cooling fluid past the major surfaces of the pancake coils.

The cooling, insulating, and bracing objectives, however, are interrelated, and care must be taken that the structures for providing one of these objectives does not deleteriously affect another objective. The electrical stresses are maximum at the inner and outer edges of the pancake coils. Oil impregnated solid insulation, such as pressboard or crepe paper, has a higher electrical strength and a higher dielectric constant than the oil itself. Thus, if the oil ducts are continued to the edges of the pancake coils, the electrical stress is transferred into the cooling ducts due to the lower dielectric constant of the oil, and ionization of the oil may occur. Thus, it is common in the prior art to place heavily taped edge shields adjacent the inner and outer edges of each pancake coil, holding them in place with tight fitting pressboard insulating channel members. This structure places an electrode having a larger radius at the coil edges, than the radius of the coil conductors, reducing the potential gradient, i.e., volts per mil, adjacent the coil edges, and also moves the oil duct away from the coil edges, which further reduces the potential gradient in the oil. This structure, howeve presents a cooling problem, and it complicates the mechanical support of the pancake coils. The cooling problem is due to the blanketing effect of the heavily insulated edge shield and tight fitting insulating channel members, which impede the transfer of heat from the conductor turns adjacent the inner and outer edges of the pancake coils to the cooling oil. The mechanical support of the coils is complicated by the fact that the insulating washer members, with insulating spacer blocks attached thereto, which separate adjacent pancake coils, must be designed such that the spacer blocks enter slots formed in the leg portions of the insulating channel members. Any misalignment between the spacer blocks and slots on the insulating channel members complicates the assembly of the pancake coils and winding, as spacer blocks which interfere with the leg portions of the channel members must be peeled off and reglued in the proper location to enter the slots in the channels. If the blocks are not replaced, the mechanical support of the pancake coils may be inadequate to prevent deformation of the conductor turns adjacent the coil edges during shortcircuit conditions.

Another limiting factor of prior art arrangements is the fact that the maximum radius of the edge shields is limited by the coil width, a factor which is becoming increasingly more important as transmission voltage levels continue to increase.

Therefore, it would be desirable to provide new and improved electrical inductive apparatus of the shell-form type which has a shielding, insulating and cooling structure for the pancake coils which provides the requisite mechanical strength for withstanding short circuit stresses, and a balanc- SUMMARY OF THE INVENTION iBriefly, the present invention is new and improved electrical inductive apparatus having at least one winding constructed of start-start, finish-finish connected pancake type coils. disposed in a tank filled with an insulating and cooling dielectric fluid, such as mineral oil. The start-start and finish-finish interpancake connections are each shielded by an edge strip assembly, Qwhich also shields the adjacent edges of both pancake coils interconnected by the interpancake connection. By shielding the edges of both pancake coils with one unitary edge shielding assembly, the effective radius of the shield is not limited by the width of a single pancake coil. Further. instead of the edge shield assembly being disposed in contact with the inner and outer edges of the pancake coi ls, it is spaced therefrom, reducing the electrical stress at the coil edges to the point where the cooling oil may contact the coil edges without ionization. The insulating spacer washer members with their spacer blocks attached may thus extend to the inner and outer edges of the pancake coils, as tight fitting insulating channel members on the edges of each pancake coil are not required. Efficient cooling of the pancake coils is maintained completely across their major surfaces, as ,well as adequate mechanical support. The assembly of the pancake coils is facilitated, as careful alignment of spacer blocks with slots in the insulating channel members is eliminated, along with the attendant hazard of losing mechanical support at the coil edges, in the event spacer blocks are not properly placed in the slots of the insulating channel members.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may be more readily understood when considered in view of the following detailed description of exemplary embodiments thereof, taken with the accompanying drawings, in which:

FIG. 1 is an elevational view, partially cut away. and partially in section, illustrating an electrical power transfon'ner of the shell-form type which utilizes the teachings of the invention;

FIG. 2 is a diagrammatic view of the electrical winding for the transformer shown in FIG. 1;

FIG. 3 is a fragmentary, cross-sectional view of the outer edges of two adjacent pancake coils constructed according to the teachings of the prior art;

FIG. 4 is a perspective view of an edge shielding assembly constructed according to the teachings of the inventioii;

FIG. 5 is a fragmentary, cross-sectional view of the edges of pancake coils for the transformer shown in FIG. I, taken through the portion of the coils which extend through the magnetic core; and 1 FIG. 6 is a fragmentary, cross-sectional view of the pancake coils shown in FIG. 5, except taken through the coils above the magnetic core.

DESCRIPTION OF THE PREFERRED EMBODIIVIENTS core-winding assembly 12 includes first and second magnetic core sections 16 and 18, respectively, each formed of a plurality of stacked metallic, magnetic laminations 20, arranged to form at least one opening for receiving electrical coils, and with the magnetic core sections being disposed in side-by-side relation to form a common winding leg portion 22. Inductive apparatus may be either single or polyphase, and of the isolated winding, or of the autotransformertype.

As illustrated in FIG. 2, the magnetic core-winding assembly 12 shown in FIG. 1 also includes a static plate 23, and a winding constructed of a stack of pancake type coils, such as pancake coils 24, 26, 28, 30, 32 and 34, all of which are arranged on a common centerline 33 and interconnected to form the winding 25 of the electrical apparatus 10. FIG. 2 is a diagrammatic view of winding 25, with only a few pancake coils being shown to simplify the drawing.

The finish" or outer turn of pancake coil 24 is electrically connected to a line terminal 35 and to the static plate 23, and adjacent pancake coils across the winding are interconnected with start-start, finish-finish connections. Specifically, pancake coils 24 and 26 are interconnected with start-start connection 36 between their innermost turns, pancake coils 26 and 28 are interconnected with finish-finish connection 38 between their outermost turns, pancake coils 28 and are interconnected with start-start connection 40 between their innermost turns, pancake coils 30 and 32 are interconnected with finish-finish connection 42 between their outermost turns, and pancake coils 32 and 34 are interconnected with start-start connection 44 between their innermost turns. The interpancake start-start, finish-finish connections provide at least one series circuit through the winding 25, with winding 25 having any number or parallel connected series circuits therethrough, depending upon the current requirements of the electrical apparatus.

Inductive apparatus 10 shown in FIG. 1 has been sectioned adjacent to pancake coil 26, as indicated by the line II in FIG. 2. The pancake coils of winding 25, such as pancake coil 26 shown in FIGS. 1 and 2, have a plurality of conductor turns 41 formed of a conductor having one or more insulated, axially spaced strands of electrically conductive material, such as copper or aluminum, which conductor is wound about a mandrel sized to provide an opening 43 for receiving leg portion 22 of the magnetic core. The turns 41 of the pancake coil define first and second major opposed surfaces 46 and 48, which are joined by the opening 43 or inside edge, and by the outside edge of the pancake coil. As illustrated in FIG. 2, certain of the pancake coils may be slightly dished to axially space the coils according to the magnitude ofthe potential difference between them.

In the prior art, the inner and outer edges of the pancake coils are each shielded with separate shielding assemblies, each having one or more solid electrical conductors which are heavily insulated and disposed in contact with the edge or edges of the pancake coil it is to shield. These prior art edge strips are held in place with tight fitting insulating channel members having slots cut in the legs thereof to accept spacer blocks disposed on the insulating spacer washer members which separate the major surfaces of adjacent pancake coils and also form cooling ducts adjacent the major surfaces of the pancake coils. For example, FIG. 3 is a fragmentary, cross sectional view of two pancake coils 50 and 52 shielded and insulated according to the teachings of the prior art with edge shielding assemblies 54 and 56, respectively. In this example, each of the edge shielding members, such as edge shielding assembly 54, have first and second solid electrical conductors 58 and 60, insulated with solid cellulosic insulating means 62,

such as paper tape. Tight fitting insulating channel members 64 and 66 are disposed about the edges of pancake coils 50 and 52, respectively, holding the edge shielding strips in the proper position. It will be noted that the leg portions of the insulating channel members, such as the leg portions 68 and 70 of insulating channel member 64, extend inwardly, covering or blanketing the major surfaces of the pancake coils adjacent their edges.

Cooling ducts adjacent the major surfaces of pancake coils 50 and 52 are provided by insulating spacer washer members having a plurality of discrete spacer block members attached thereto in a pattern which includes blocks aligned to enter slots formed in the legs of the channel members. For example, spacer washer members 72 and 74 are disposed to provide cooling ducts 76 and 78 adjacent pancake coils 50 and 52, respectively, with washer member 72 having a plurality of spacer blocks which form cooling duct 76, such as spacer block 82 which enters slot 83 in the leg of insulating channel member 64 and with washer member 74 having a plurality of spacer blocks, which form cooling duct 78, such as spacer block 86 which enters slot 87 in insulating channel member 66. Blocks 82 and 86 must be aligned with the slots 83 and 87, respectively, formed in the adjacent legs of the insulating channel members. If they are misaligned they must be peeled off and reglued in the proper location, which complicates assembly of the winding. 1f the peeled blocks are inadvertently not repositioned, the pancake coils may not have adequate support against short circuit forces. Spacer blocks are also required between the leg portions of the insulating channel members, and the washer members 72 and 74, to provide support between the slots in the channel members, such as blocks and 84, which are disposed on the channel members, between the slots, and which have substantially the same length dimension as the channel legs. Further, it is elear that the leg portions of the tight fitting insulating channel members provide a blanketing effect about the edges of the pancake coils, which impedes the transfer of heat flow from the conductor turns adjacent the leg portions to the oil flowing through the cooling ducts.

This invention solves these problems encountered in prior art structures by an entirely different approach to the edge shielding problem, shielding adjacent edges of two pancake coils simultaneously with a single unitary assembly, as well as shielding the interpancake connection adjacent these edges. Further, the edge shielding assembly is spaced from the edges of the coils it is to shield, instead of being in adjacent contacting relation therewith. This structure allows the spacer blocks fixed to the insulating spacer washer members to extend completely to the inner and outer edges of the pancake coils, providing cooling ducts which efficiently remove heat from all of the conductor turns of the pancake coils. This structure further provides mechanical support for the coils completely across their major surfaces, including providing support for the conductor turns immediately adjacent the inner and outer edges of the pancake coils, without the requirement of intermeshing spacer blocks in slots formed in the insulating channel members.

As shown in FIG. 2, edge shield assembly 90 is disposed to shield the outer edges of pancake coil 24 and static plate 23, edge shielding assembly 92 is disposed to shield the start-start connection 36 and the inner edges of pancake coils 24 and 26, edge shielding assembly 94 is disposed to shield the finishfinish connection 38 as well as the outer edges of pancake coils 26 and 28, edge shielding assembly 96 is disposed to shield the start-start connection 40 as well as the inner edges of pancake coils 28 and 30, edge shielding assembly 98 is disposed to shield the finish-finish connection 42, as well as the outer edges of pancake coils 30 and 32, edge shielding assembly 100 is disposed to shield the start-start connection 44, as well as the inner edges of pancake coils 32 and 34, and edge shielding assembly 104 is disposed to shield the outer edge of pancake coil 34. Each of the edge shielding assemblies is electrically connected to the interpancake connection it is shielding. For example, edge shielding assembly 90 is connected to terminal 35, edge shielding assembly 90 is connected to terminal 35, edge shielding assembly 92 is connected to the startstart connection 36, edge shielding assembly 94 is connected to the finish-finish connection 38, edge shielding assembly 96 is connected to the start-start connection 40, edge shielding assembly 98 is connected to the finish-finish connection 42, edge shielding assembly 100 is connected to the start-start connection 44, and edge shielding assembly 104 is connected to lead 105.

The inner edge of the static plate 23 may be shielded in a conventional manner with a shielding assembly 102, as it does not have the cooling and support problems associated with the pancake coils. The last pancake coil in the stack of pancake coils, such as pancake coil 34, has its outer edge shielded with an assembly 104. Assembly 104 may shield only this edge, if this coil is connected to ground; or, if the winding is part of a three-phase delta connection, assembly 104 may also shield in adjacent edge of another static plate.

As illustrated in FIG. 1, the insulating washer members disposed between pancake coils, such as insulating washer member 106, may extend completely to theinner and outer edges of the pancake coils, and spacer blocks attached to the side of the washer member facing the adjacent major surface of the pancake coil, such as spacer blocks 108, may extend completely to the inner and outer edges of the pancake coil. Insulating channel members are disposed about the edges of both pancake coils shielded by the edge shielding assemblies, with the outer edges of pancake coils 26 and 28 having a plurality of insulating channel members, such as channel member 110. The legs of the channel members extend over the outer surfaces of the spacer washer members, such as over spacer washer member 106. In like manner, a plurality of insulating channel members are disposed about the inner edges of pancake coils 24 and 26, such as channel members indicated generally at 112. The channel members 112 are shown in section, since a view of section taken through winding 24 along line I-I in FIG. 2 cuts these insulating channel members along the back portions of the channels.

This new edge shielding structure is made possible by a new edge shielding assembly 120 shown in FIG. 4, which may be used for both the inner and outer edge shielding assemblies shown in FIGS. 1 and 2, such as the inner and outer edge shielding assemblies 92 and 94 shown about the inner and outer edges ofpancake coil 106.

Edge shielding assembly I includes first and second shielding members 122 and 124, respectively, each of which have an insulating core member 126 and 128, respectively, and electrically conductive means 130 and 132, respectively, disposed about the core members. Insulating means 134 and 136 are disposed about the electrical conductor means 130 and 132, respectively, such as paper tape, and spacer means 140 is disposed between the first and second shielding members 122 and 124. Spacer means 140 have a width dimension selected to enable the first and second shielding members to properly shield the outermost edges of two adjacent pancake coils, as will be hereinafter explained. Insulating means 142 is disposed about thefirst and second shielding members 122 and 124 and the spacer means 140, which may be paper tape, or the like, wrapped tightly about the first and second shielding members to provide a unitary assembly which may be placed in the desired spaced relation with the inner and outer edges of adjacent pancake coils.

The electrically conductive means 130 and 132 must not only have a smooth curved surface, but it must provide a curved surface of large radii without unduly increasing the thickness dimension of the resulting edge shielding assembly. As illustrated in FIG. 4, an elliptical or substantially elliptical cross-sectional configuration has been found to be excellent for this application. 7

Since the edge shielding assembly must be flexible enough to enable it to easily conform to the configuration of the outer and inner edges of the pancakecoils, the selection of the Components for shielding assembly 120 must achieve this result. Thus. the ropelike insulating core members 126 and 128 must be formed of flexible material which will maintain the desired cross-sectional configuration of the electrical conductor means disposed thereon. Silicon rubber has been found to be excellent for this purpose.

The electrically conductive means 130 and 132 is preferably formed of a flexible, braided conductor which is woven tightly about the insulating core members 126 and 128, respectively. The braided or woven conductors of which electrically conductive means 130 and 132 are formed have a large plurality of relatively fine metallic wires or strands, with the portion of electrically conductive means within circle 144 being shown magnified within circle 44' to more clearly illustrate the strands 146 of a woven wire construction which is suitable. The direction of the individual wires or strands 146 form a substantial angle with respect to the longitudinal dimension of the insulating core member 126, to allow the first and second shielding members 122 and 124 to be easily shaped to conform to the desired contours, and to allow the length of the edge shielding means to change along with any changes in the dimensions of the pancake coils during the various manufacturing steps in the construction of an electrical winding.

While the diameter of the individual strands 146 is not critical, the diameter should be selected to be as small as practical. Very small or fine diameter strands provide a substantially smooth outer surface on the resulting woven conductor, which is necessary in order to reduce the potential gradient at its surface below the corona inception level. Fine strands also add to the flexibility of the edge strip, facilitating its handling and bending. Further, fine strands are individually so flexible that any broken ends that may extend outwardly from the surface of the woven conductor will be bent inwardly to conform to the surface of the conductor when the braided conductor is subsequently insulated. This is important, as outwardly extending wires or strands may cause the formation of corona. Small diameter strands also aid the structure electrically, as reducingthe diameter of the strands increases their resistance to the flow of electrical current. Small diameter strands also allow more strands to be utilized in the braid, which reduces the magnitude of circulating currents due to the larger number of contacts between the strands.

Copper wire strands, each having a diameter of 0.0063 inch are suitable for the woven conductor, but other diameters and other metals, such as aluminum, stainless steel, and the like, may be used. When higher resistivity materials are used,thc circumferential dimension of the electrically conductive means may be increased without resulting in excessive losses due to eddy and circulating currents.

FIGS. 5 and 6 are fragmentary, sectional views of the outer edges of pancake coils 26, 28, 30 and 32 shown in FIGS. 1 and 2, utilizing the new edge shielding structure shown in FIG. 4. FIG. 5 is a view of the pancake coils as they pass through the iron of the magnetic core, and FIG. 6 is a view of the pancake coils at their upper ends above the core iron.

More specifically, FIG. 5 illustrates the ends of pancake coils 26, 28, 30 and 32, with only one of the conductor turns of pancake coil 26 being sectioned and detailed, as the other turns would be similar. As illustrated, each conductor turn, such as turn 150 in pancake coil 26, may include two parallel connected electrical conductors 152 and 154, each of which may be individually insulated with insulating means 154, such as paper tape, and then the whole assembly insulated with insulating means 156, which may also be paper tape, to provide a unitary conductor assembly which may be wound to provide the pancake coil.

Cooling ducts are provided adjacent each major surface of the pancake coils, with cooling ducts I60 and 162 being formed adjacent the major surfaces 46 and 48 of pancake coil 26 by insulating spacer washer members 106 and 164, respectively, each of which have a plurality of discrete spacer block members attached thereto, such as spacer blocks 108, which space the insulating washer members from the pancake coils and establish the cooling ducts. It will be noted that the insu- The first and second shielding members of each edge shielding assembly are spaced such that they extend to, or slightly past the two outermost major surfaces of the two pancake coils it is shielding, depending on the specific application. If the potential gradient is reduced to the desired magnitude by aligning the edges of the shields with the outer major surfaces of the two adjacent pancake coils, this would be the preferred construction as it would keep the coil stack dimension as small as possible, but in some applications it may be necessary to extend the shields past the outer surfaces of the two adjacent pancake coils to obtain the desired potential gradient. The edge shielding assembly reduces the electrical stresses at the edges of the pancake coils below the ionization level of the oil, allowing the oil to flow freely about the edges of the pancake coils. The high electrical stresses on the first and second shielding members of the edge strip shielding assembly may As illustrated in FIG, 6, free flow of coolant past the major.

surfaces of the pancake coils is achieved by forming openings through the outer edge shielding assemblies, at both the bottom and top edges of the pancake coils. Openings are also formed in the insulating channel members which hold the edge shielding assemblies in place. For example, openings 174 and 176 are formed in the outer insulating means 142 of the edge shielding assembly, an opening 178 is formed in the spacer means I40 of the edge shielding assembly, and an opening 180 is formed in the insulating channel member 172 in alignment with the openings in the spacer means and in the insulating means of the edge shielding assembly. Thus, cooling oil may flow. as illustrated by the arrows in FIG. 6, past the major surfaces of the pancake coils, through the edge shielding assemblies. The electrical stresses between the two shielding members of an edge shielding assembly is relatively low, enabling the openings to be formed between them to allow oil flow without danger ofionizing the oil. The arrows in HO. 1 illustrate relatively cool oil entering the ducts at the lower ends of the pancake coils, moving upwardly through the ducts adjacent the major surfaces of the pancake coils, and exiting at the upper ends of the coils where the oil is directed to heat exchanger means (not shown), for removal of the heat therefrom.

In summary, there has been disclosed new and improved electrical inductive apparatus, such as an electrical power transformer, which has its cooling efficiency improved without deleteriously affecting the manufacturing or assembly of the apparatus, and without deleteriously affecting the mechanical support of the pancake coils necessary to withstand short circuit stresses. A new and improved edge shielding assembly is disclosed for electrically shielding the edges of the pancake coils of the apparatus, with the new and improved shielding assembly simultaneously shielding the edges of two adjacent pancake coils, as well as shielding the interpancake connection adjacent the coil edges. The new and improved edge shielding assembly is spaced from the inner and outer edges of the pancake coils, reducing the electrical stresses adjacent the edges of the pancake coils to the point where the cooling oil may safely come into contact therewith, efficiently cooling the pancake coils completely across their major surfaces. The disclosed construction does not require the spacer blocks on the insulating spacer washer members to be intermeshed with slots formed in insulating channel members, thus facilitating the manufacturing of the inductive apparatus, and there is no danger of loss of mechanical support at the coil edges due to the peeling of misaligned blocks and the subsequent failure to reglue the blocks in the required position. Finally, by shielding the edges of two adjacent pancake coils, the radii of the electrically conductive portions of the edge shielding assemblies may be selected to reduce the potential gradient to the desired level, without limitation by the width dimension of a pancake coil.

I claim as my invention:

1. Electrical inductive apparatus comprising:

a tank,

fluid cooling means disposed in said tank,

an electrical winding disposed in said tank and immersed in said fluid cooling means, said electrical winding including a plurality of axially spaced pancake-type coils each having a plurality of conductor turns which define first and second major opposed surfaces, an opening which extends between its major surfaces, and inner and outer edges,

means electrically interconnecting adjacent pancake coils, providing interpancake connections which alternately connect the pancake coils with start-start and finish-finish connections and provide at least one series circuit through the electrical winding,

a plurality of insulated edge shielding assemblies, each disposed to shield one of the interpancake connections and the adjacent edges of the two pancake coils interconnected thereby,

each of said plurality of insulated edge shielding assemblies including first and second shielding members, each of which have an insulating core member and electrically conductive means disposed about said core member, first spacer means disposed between said first and second shielding members, and insulating means disposed about said first and second shielding members and said first spacer means, to provide a unitary edge shielding assembly,

and second spacer means disposed between the inner and outer edges of said pancake coils and their associated edge shielding assemblies, enabling said fluid cooling means to come into contact with the inner and outer edges of said pancake coils.

2, The electrical inductive apparatus of claim 1 including means connecting the electrically conductive means of the first and second shielding members of each of the plurality of edge shielding assemblies to the interpancake connection the edge shielding assembly is shielding.

3. The electrical inductive apparatus ofclaim 1 wherein the insulated edge shielding assembly disposed about the outer edges of the pancake coils has a plurality of openings therethrough which extend between the first and second shielding members, with said plurality of openings being disposed to enable the fluid cooling means to establish an upward flow path between adjacent pairs of pancake coils.

4. The electrical apparatus of claim 1 wherein the first spacer means in each of the insulating edge shielding assemblies includes a strip ofcorrugated insulating material.

5-. The electrical apparatus of claim 1 wherein the electrically conductive means disposed on the insulating core members of the first and second shielding members includes a plurality of electrically conductive strands woven together about its associated insulating corc member to provide a substantially smooth outer surface.

6. The electrical inductive apparatus of claim 1 including a plurality of discrete spacer block members disposed adjacent to, and in contact with, the first and second major opposed surfaces of the pancake coils, insulating washer members disposed in spaced relation with the major surfaces of the pancake coils, with one of its surfaces being in contact with the spacer block members, and insulating channel members disposed about each of the plurality of insulated edge shielding assemblies, with the leg portions of the insulating channel members contacting the surfaces of certain of said insulating washer members, which surfaces are opposite to the surfaces which are in contact with the spacer block members.

7? The electrical inductive apparatus of claim 1 wherein the first and second shielding members extend at least to the oufirst spacer means is sized to space the first and second shieldtermost major surfaces of the two adjacent pancake coils the ing members of each edge shielding assembly such that the edge shielding assembly is associated with. 

1. Electrical inductive apparatus comprising: a tank, fluid cooling means disposed in said tank, an electrical winding disposed in said tank and immersed in said fluid cooling means, said electrical winding including a plurality of axially spaced pancake-type coils each having a plurality of conductor turns which define first and second major opposed surfaces, an opening which extends between its major surfaces, and inner and outer edges, means electrically interconnecting adjacent pancake coils, providing interpancake connections which alternately connect the pancake coils with start-start and finish-finish connections and provide at least one series circuit through the electrical winding, a plurality of insulated edge shielding assemblies, each disposed to shield one of the interpancake connections and the adjacent edges of the two pancake coils interconnected thereby, each of said plurality of insulated edge sHielding assemblies including first and second shielding members, each of which have an insulating core member and electrically conductive means disposed about said core member, first spacer means disposed between said first and second shielding members, and insulating means disposed about said first and second shielding members and said first spacer means, to provide a unitary edge shielding assembly, and second spacer means disposed between the inner and outer edges of said pancake coils and their associated edge shielding assemblies, enabling said fluid cooling means to come into contact with the inner and outer edges of said pancake coils.
 2. The electrical inductive apparatus of claim 1 including means connecting the electrically conductive means of the first and second shielding members of each of the plurality of edge shielding assemblies to the interpancake connection the edge shielding assembly is shielding.
 3. The electrical inductive apparatus of claim 1 wherein the insulated edge shielding assembly disposed about the outer edges of the pancake coils has a plurality of openings therethrough which extend between the first and second shielding members, with said plurality of openings being disposed to enable the fluid cooling means to establish an upward flow path between adjacent pairs of pancake coils.
 4. The electrical apparatus of claim 1 wherein the first spacer means in each of the insulating edge shielding assemblies includes a strip of corrugated insulating material.
 5. The electrical apparatus of claim 1 wherein the electrically conductive means disposed on the insulating core members of the first and second shielding members includes a plurality of electrically conductive strands woven together about its associated insulating core member to provide a substantially smooth outer surface.
 6. The electrical inductive apparatus of claim 1 including a plurality of discrete spacer block members disposed adjacent to, and in contact with, the first and second major opposed surfaces of the pancake coils, insulating washer members disposed in spaced relation with the major surfaces of the pancake coils, with one of its surfaces being in contact with the spacer block members, and insulating channel members disposed about each of the plurality of insulated edge shielding assemblies, with the leg portions of the insulating channel members contacting the surfaces of certain of said insulating washer members, which surfaces are opposite to the surfaces which are in contact with the spacer block members.
 7. The electrical inductive apparatus of claim 1 wherein the first spacer means is sized to space the first and second shielding members of each edge shielding assembly such that the first and second shielding members extend at least to the outermost major surfaces of the two adjacent pancake coils the edge shielding assembly is associated with. 